1. Field of the Invention
The present invention relates to radio frequency (RF) switches. More specifically, the present invention relates to RF micro-magnetic latching switches with magnetic and electrostatic actuation mechanisms.
2. Related Art
Switches are typically electrically controlled two-state devices that open and close contacts to effect operation of devices in an electrical or optical circuit. Relays, for example, typically function as switches that activate or de-activate portions of electrical, optical or other devices. Relays are commonly used in many applications including telecommunications, radio frequency (RF) communications, portable electronics, consumer and industrial electronics, aerospace, and other systems. More recently, optical switches (also referred to as xe2x80x9coptical relaysxe2x80x9d or simply xe2x80x9crelaysxe2x80x9d herein) have been used to switch optical signals (such as those in optical communication systems) from one path to another.
Although the earliest relays were mechanical or solid-state devices, recent developments in micro-electro-mechanical systems (MEMS) technologies and microelectronics manufacturing have made micro-electrostatic and micro-magnetic relays possible. Such micro-magnetic relays typically include an electromagnet that energizes an armature to make or break an electrical contact. When the magnet is de-energized, a spring or other mechanical force typically restores the armature to a quiescent position. Such relays typically exhibit a number of marked disadvantages, however, in that they generally exhibit only a single stable output (i.e., the quiescent state) and they are not latching (i.e., they do not retain a constant output as power is removed from the relay). Moreover, the spring required by conventional micro-magnetic relays may degrade or break over time.
Another micro-magnetic relay is described in U.S. Pat. No. 5,847,631, (the ""631 patent) issued to Taylor et al. on Dec. 8, 1998, the entirety of which is incorporated herein by reference. The relay disclosed in this patent includes a permanent magnet and an electromagnet for generating a magnetic field that intermittently opposes the field generated by the permanent magnet. The relay must consume power in the electromagnet to maintain at least one of the output states. Moreover, the power required to generate the opposing field would be significant, thus making the relay less desirable for use in space, portable electronics, and other applications that demand low power consumption.
The basic elements of a micro-magnetic latching switch include a permanent magnet, a substrate, a coil, and a cantilever at least partially made of soft magnetic materials. In its optimal configuration, the permanent magnet produces a static magnetic field that is relatively perpendicular to the horizontal plane of the cantilever. However, the magnetic field lines produced by a permanent magnet with a typical regular shape (disk, square, etc.) are not necessarily perpendicular to a plane, especially at the edge of the magnet. Then, any horizontal component of the magnetic field due to the permanent magnet can either eliminate one of the bistable states, or greatly increase the current that is needed to switch the cantilever from one state to the other. Careful alignment of the permanent magnet relative to the cantilever so as to locate the cantilever in the right spot of the permanent magnet field (usually near the center) will permit bi-stability and minimize switching current. Nevertheless, high-volume production of the switch can become difficult and costly if the alignment error tolerance is small.
What is desired is a latching switch usable for RF signal applications. Such a switch should also be reliable, simple in design, low-cost and easy to manufacture, and should be useful in a variety of environments.
Micro-machined RF switches having enhanced electrical and mechanical characteristics are described. The micro-machined RF switches include a substrate, a moveable micro-machined cantilever supported by the substrate, and an actuation mechanism that causes the cantilever to switch between two or more states. In one aspect, in a first state, a conducting layer of the cantilever couples a RF transmission line to a reference signal. In a second state, the conducting layer does not couple the RF transmission line to the reference signal. In further states, the conducting layer can couple one or more additional RF transmission lines to respective reference signals.
In a further aspect, the present invention is directed to a micro-machined RF switch with an electromagnetic actuation mechanism. A moveable micro-machined cantilever is supported by a substrate. The cantilever has a magnetic material and a longitudinal axis. The cantilever also has a conducting layer. A first permanent magnet produces a first magnetic field. The first magnetic field induces a magnetization in the magnetic material. The magnetization is characterized by a magnetization vector pointing in a direction along the longitudinal axis of the cantilever. The first magnetic field is approximately perpendicular to the longitudinal axis. An electromagnet produces a second magnetic field to switch the cantilever between a first stable state and a second stable state. A temporary current through the electromagnet produces the second magnetic field such that a component of the second magnetic field parallel to the longitudinal axis changes direction of the magnetization vector, thereby causing the movable element to switch between the first stable state and the second stable state. In the first stable state, the conducting layer couples a RF transmission line to a reference signal. In the second stable state, the conducting layer does not couple the RF transmission line to the reference signal.
In another aspect, the RF switch includes a torsion spring that supports the cantilever on the substrate. The torsion spring flexes to allow the cantilever to move.
In another aspect, in the second stable state, the conducting layer couples a second RF transmission line to a second reference signal.
In another aspect, in the first stable state, a first portion of the conducting layer connects the first RF transmission line to the first reference signal, and in the second stable state, a second portion of the conducting layer connects the second RF transmission line to the second reference signal.
In another aspect, a first portion of the cantilever flexes to enhance coupling of the first RF transmission line to the first reference signal by the conducting layer, and/or a second portion of the cantilever flexes to enhance coupling of the second RF transmission line to the second reference signal by the conducting layer.
In another aspect, the cantilever includes a first angled portion to enhance coupling of the first RF transmission line to the first reference signal by the conducting layer, and/or the cantilever includes a second angled portion to enhance coupling of the second RF transmission line to the second reference signal by the conducting layer.
In still another aspect, the present invention is directed to a micro-machined RF switch with an electrostatic actuation mechanism. A moveable micro-machined cantilever is supported by a substrate. The cantilever has a conducting layer. The cantilever is switchable to at least a first state and a second state. A gate metal is formed on a surface of the substrate proximate to the conducing layer. A voltage applied to the gate metal produces an electrostatic attraction between the gate metal and the conducting layer. The cantilever is thereby caused to switch to the first stable state. In the first state, the conducting layer couples a RF transmission line to a reference signal. In the second state, the reference signal is decoupled from the first RF transmission line.
In another aspect, a second gate metal is formed on a surface of the substrate proximate to the conducting layer, on a side of the torsion spring opposite the first gate metal. A voltage applied to the second gate metal produces an electrostatic attraction between the second gate metal and the conducting layer. The cantilever is thereby caused to switch to a third state. In the third state, the conducting layer couples a second RF transmission line to a second reference signal. In the second state, the conducting layer is decoupled from the first and second RF transmission lines.
In another aspect, a first portion of the cantilever flexes to enhance coupling of the first RF transmission line to the first reference signal by the conducting layer, and/or a second portion of the cantilever flexes to enhance coupling of the second RF transmission line to the second reference signal by the conducting layer.
In another aspect, the cantilever includes a first angled portion to enhance coupling of the first RF transmission line to the first reference signal by the conducting layer, and/or the cantilever includes a second angled portion to enhance coupling of the second RF transmission line to the second reference signal by the conducting layer.
The micro-magnetic latching switches of the present invention can be used in a plethora of products including household and industrial appliances, consumer electronics, military hardware, medical devices and vehicles of all types, just to name a few broad categories of goods. The micro-magnetic latching switches of the present invention have the advantages of compactness, simplicity of fabrication, and have good performance at high frequencies, which lends them to many novel applications in many RF applications.
These and other objects, advantages and features will become readily apparent in view of the following detailed description of the invention.